Go to Poloniex
Log in or create a new account on https://poloniex.com/.
Follow to API
Hover the settings icon on the top right corner, click "API Keys."
If you see the message about disabled API access, click "Enable API" then confirm with 2FA and email.
Click "Create New Key"
Confirm with 2FA and email
Add Poloniex to 3Commas
Don't change the key settings.
Check how to connect API to 3Commas.