Open the program on your computer and log in using your official MyHeritage email and password.

Linking Matches On Your MyHeritage Family Tree – Help | FamilyTreeDNA

MyHeritage Family Tree Builder Premium is a robust genealogy software. One interesting feature I found is:

Even though the Premium link syncs your tree to the cloud, always keep a local backup file (.ZED format) on an external hard drive.

Be cautious of third-party websites offering "cracked copies," "free premium serial keys," or "direct premium download links."