Recommendations for new users

I’m sorry if this has been asked before, or if it’s obvious
but:

I’m trying to make a deep learning model that can recommend
items to users based on the rating that they’ve given other
items.

And I kind of understand how to do this.

But now comes the part that confuses me, let’s say I deploy this
model on my website. But then an existing user rates some new items
or what if it’s an entirely new user that is not known by the
model? Do I then need to retrain my entire model?

Or is there some way to make a recommender model that can make
recommendations for users without retraining the entire model
again?

I’ve tried googling this, but I can’t seem to find an answer
anywhere(or I’m not searching for the right words)

Anyone have a suggestion that can push me in the right
direction?

Thanks in advance!