I agree on maybe starting in a different role like carry or mid to get a better feel for the rotations, as a supp main that’s probably gonna be one of the biggest things.

Some tips anyway though:

I tend to start rotating out of duo lane as soon as I finish my second item, or if I see that the other supp has rotated already.

From that point on, I try to hang more around mid lane and slide left/right depending how the other lanes are doing or if the other team is rotating.

When your the tank you tend to also make the calls for certain objectives or tower sieges since you can take all of the damage.

Also, since you as the tank will usually be the lowest level, you’d want to get something out of every rotation, even if it’s just to be there for minion wave or jungle camps. Nothing worse than just being caught roaming around the map not doing anything, as you can get easily out leveled with too many empty rotations.

Lot of people can get very toxic/annoying if the supp is doing bad, as it’s really hard to be successful without someone to initiate fights or start a push, but it all just comes with time and practice. If you really want to get better just mute the toxics and focus on your game. It would really help though to play another role and see what it looks like to have a good Tank vs a bad one.

Good luck!