@leonardochen0 wrote:
You could issue commands for each motor M1/M2 with different speeds...
Maybe make a custom block (function) "Move forward" with speeds that work for you.
If you feel like hacking a bit...
You could change the definition of what "Move forward" means. In OSX, the file ismBlock.app/Resources/ext/libraries/mbot/js/mbot.js
In line 89 I see some references that you could change.