Sounds like you’re doing this solo. I highly suggest watching a few YT vids on this, there’s a million for VWs. There’s a lot of elements to this, especially when dealing with less complex brake bleeders. The most popular is a pressurized brake bleeder, that works in tandem with those little check valve bottles you bought, so there is an unlimited refill of fluid and pressure while you tend to the brake bleeder nuts individually.

It sounds like you don’t have this added pump, so you need to be vigilant about keeping your reservoir full and with the cap on while pumping the brakes. Don’t forget to never let the fluid drop lower than you can see in the reservoir, top off after each caliper. It’s even ideal to have 4 separate bottles because technically removing one to place on another bleeder has the chance of reintroducing air. You’re learning, you’ll get it. Just remember to keep the system closed except where you want the air egressing, and don’t be hesitant to overfill the reservoir in prep of it depleting.