I have searched Google Accounts and Google Sites services. Nowhere was I able to find anything relating to any domain settings. Only thing I found about domain transfer was in Google Domains, but it does not work in Finland.
Domain transfers are done by the receiving registrar. You get in touch with them and provide them with the domain information and state that you want to transfer it in to them from an alternate registrar and they will contact the registrar to transfer the domain. There is no fixed form to do from Google's end. What you will probably need to do (going generic here as I am not familiar with the specifics of the Finnish domain system) is lodge a support request for Google domain's requesting the transfer code and requesting client transfer be enabled, and with that information the receiving registrar will be able to transfer the domain to their servers.
I should note that this does not transfer the hosted website itself though, only the domain name. If you wish to transfer the site itself you will need to do that yourself and it ios beyond the scope of this question to go into that.