If you wish to start sending mail using an alias (Google), no changes are needed on your end. (If you want to report on number of emails that alias has sent, you'll need to add the alias a Pipeline 'Guest').
Streak Pipelines and Contacts belong to your Streak Team and not to an individual email address. If you're currently using your personal email address to access Streak and want to switch to using a different existing email account like your your business address (or using with a personal and want to switch to a different personal email address) follow these steps:
Open the Gmail / G Suite account that you currently use to access the Pipeline(s)
Add the new address to your Streak team as a Team Owner (can add/remove users)
Add the new address to your Streak Pipeline as a Pipeline Owner (can manage all aspects of that specific Pipeline)
Optionally, remove your old address from the Pipeline
Optionally, remove your old address from the Team
Note that the Free Plan does not allow sharing of a Pipeline.