Yep this guide should help you with the specifics of how to import them: https://help.klaviyo.com/hc/en-us/articles/115005078487-How-to-migrate-existing-email-subscribers-and-unsubscribes-into-Klaviyo

Hello Brett thank you very much for your help!
i might have not properly explained what i meant though. 
The question is this: we are running a sweepstake contest through our partner brand website (which is not connected to our klaviyo) since the sweepstake is for our brand but not directly collected by us, are we allowed to upload those emails to our klaviyo without breaking the policy? and what need to be done in order to be compliant?

Hello @Li Lar,

I would suggest checking out our Understanding compliant lists Help Center article which explains a bit more on this. 

So long as these sweepstake contestants are fully aware and have shared explicit consent to opt into your marketing list for your specific brand, I don’t see why you’d be violating Klaviyo’s terms of service. 

David