It’s actually Content=> Menus=> URL redirects.
Obviously, this should be setup in the old store.
And obviously, you’d need your old store alive for the redirects to work.
However, this would not really work, as redirects only apply to pages which can not be rendered in a normal way, so, basically, if you have a live
oldstore.com/products/t-shirt, yes you would be able to create a redirect from this URL to a new one, but it would not work, so you’d need to unpublish this product for the redirect to work.
Lots of manual work.
In my opinion this it not the best way though – you can rather move your domain(s) from the old store to the new one.
If you set it up it as a secondary domain which redirects to the primary one most of your redirects would happen automatically and you would only need to set up manual redirects for those products/collections/pages which have their handle changed.
May actually not need any of those at all.
Your old store would still be reachable via its myshopify.com address if you need it.
https://help.shopify.com/en/manual/online-store/menus-and-links/url-redirect
https://help.shopify.com/en/manual/domains/domain-type/change-primary-domain