This is going to be the shortest guide ever on Mystrika.
Answer is you don't enable warmup on Mystrika.
As soon as, an Email Address is connected to Mystrika (on "Home" tab), warmup automatically gets enabled.
You can tune the warmup settings by going to,
"Home" > Click "four dots" > Warmup settings.
Mystrika automatically ensure proper gap between re-using your SMTP server (minimum of 4 minutes gap) and randomizer on top of it.
To take things further, read emulation and other settings are already taken care of, with randomization, ensuring you are in capable hands.