Hi @Laurent,

Thanks for sharing to the Community. 

Your first step would be to integrate Klaviyo with Typeform so that your customers that complete actions or opt in to subscribe to a newsletter can be found within the Klaviyo platform.

You can point your Typeform form to your Newsletter list in Klaviyo so they trigger your normal flow:​
Another option you have would be to clone your Welcome Series flow (if you have one) and have it trigger off of your newsletter list. If you chose this option, I would suggest adding an additional filter to exclude anyone that has also subscribed to the Newsletter list; this is because you don't want them to receive duplicate emails.
A third option is to create a segment of profiles that are in your Newsletter list or have filled out the form and trigger your welcome series off of the segment. Typically, we don't suggest using a segment to trigger a flow if you can help it, since there are a lot of moving pieces with a segment triggered flow.

Let me know if that helped,

Alex