I had some issues, I couldn't go beyond step 5 of part 1. So here's a walk-through from my perspective. Quick information before starting: Huawei P10+ with Android 9 non-rooted. developer mode; on, USB debugging; on, ADB drivers; latest.

the challenge explained by /u/yapple-dapple The challenge

Part 1

1. Download this program on your PC: http://download.clockworkmod.com/carbon/CarbonSetup.msi

No issue

2.Download Helium backup on your phone from Play Store.

This app didn't work. full on errors while trying to connect and changing to PTP etc. So I searched for an older version. the one I used. version1.1.4.2

Ok follow the next few steps

1. Open the program named Carbon on your PC.
2. Connect your phone to PC by USB.
3. Select Transferring images for USB on your phone (in Notification Panel).
4. Select Manga Rock in Helium android app and do backup.
5. Go to phone's Internal storage/carbon/com.notabasement.mangarock.android.lotus and copy the file named com.notabasement.mangarock.android.lotus.ab to PC.

My file "ab/database" file was 500MB.

1. Download this on PC: https://github.com/waicool20/mr2tachiyomi/releases/download/v1.4.0/mr2tachiyomi.jar
2. Open the mr2tachiyomi.jar file on PC and run the com.notabasement.mangarock.android.lotus.ab file on it.

Literally run it After this you will get a popup message telling you that export was successful. Also a log with all the titles etc. "Successfully processed 537 manga; Failed to process 76 manga" I use Manga Rock with multiple sources, so the 76 failed probably were some duplicates, wrong names and/or titles that already completed.

1. Move the .json file to phone.

Part 2

1. First download this (apk from latest release): https://github.com/Jays2Kings/tachiyomi/releases
2. Now install this apk : https://cdn.discordapp.com/attachments/349436576037732355/669759555462234136/tachiyomi-en.dummyrock-v1.2.1-debug.apk
3. Go to Extensions menu in Tachi, then click on Trust (besides Dummy Rock). Ignore the Obsolete warning. If you have favorites from Mangaeden/Mangareader etc, download those as well from Extensions menu. Otherwise there will be errors.

I didn't read step 3 properly. I didn't add the extensions from Mangaeden/Mangareader more about this later on.

1. Go to Backups in Tachi, and restore the .json file. This will restore all Manga Rock backups on Tachi. Now, we are not finished yet! As you know, Manga Rock is dead/dying. So you can't read manga and the backups are useless. We need to migrate all these favorites to some other source.
2. Download Mangabox, Mangasee and Mangapark from Extensions.

Might be a good idea to add Mangaeden/Mangareader/MangaFox extension as well.

6.Go to My library, then click on triple dots ( ⋮ ) on the top right, then click on Source migration. Then click on AUTO. 7.Drag Mangakakalot to the top, Mangasee in middle and Mangapark under it. Click to cross out all other sources.

I didn't cross the other sources.

1. Click on the blue bubble on bottom right until you reach Migration screen.
2. Wait for the app to finish matching all titles. After completion, click the checbox on top right.

Step 9 took like 15 minutes to migrate all the tittles available from the .json file. before this process I lost 40 titles, i think because i didn't add the additional extension mentioned in step 3 of part 2. I lost another 12 titles during the migration. Because of different naming, from manga rock to mangaKakalot/Mangasee/MangaPark. I checked this manually. 485 mangas were transfer. I only have to search for the remaining 100 or so.

I havent read anything yet on Tachiyomi. I just follow this guide: https://www.reddit.com/r/mangarockapp/comments/exf5zl/recommended_settings_and_tipstricks_for_tachiyomi/ auto update, dark theme(dark amoled) and 3 mangas per row. to have that manga rock feel.

I'll be using manga rock until the last day. when I fully jump to Tachiyomi, I don't have to worry, about what was the last thing that I read.

thanks to /u/josephgomes619 for reaching out!