There is a bug in one of the latest Android release where you can only edit tabs when you put the project in Play mode.
With it in Play mode double-tap the active tab and you’ll be able to edit it.
@BlynkAndroidDev in Android Beta 2.28.0 (07.05.20 18:29:59) this issue is fixed, but now you can’t edit tabs in either Play or Edit mode!
Pete.