Warning - sending out cold emails without an opt-out link isn't recommended for various reasons as it is not legal to send cold emails without an opt-out link in few countries.
Optout link can be enabled from Sequence settings. Outplay allows you to update the opt-out link as well.
To enable an opt-out link :
Click on any sequence from the sequences list page.
Go to settings.
Check-in Include an opt-out link.