Install Ubisoft connect from the https://www.ubisoft.com/ website, you will need to log into the platform (you can use your old Uplay account log in I think) and then go to installed games on the ubisoft connect panel and you can the update the game from there. It should then be playable through steam.

tried it but stuck on pages that says "static3.cdn.ubi.com refused to connect."
i guess people on SEA can't, i've check other guides and it says it might need VPN

Uninstall Uplay and Install Ubi Connect.

for some unknown reason, i can't download ubi connect, it's been a while now

Try to download it directly from this Ubi' Con[ubisoftconnect.com] link to see if solves your issue.
And if not, then the other only gruesome option that I can phantom is having to go to Ubi$oft's "Support" site[www.ubisoft.com] and open a ticket for this. And just let me warn you beforehand to expect some darned aweful, 'so called' dictatorial entitled kind of support from most of its staff.