Global or privileged role admin prerequisite
You must be a global or privileged role admin to consent to the Microsoft 365 permission sets.
If you don't have that access level, you can send a global or privileged role admin the following article specifying the name of the Enterprise application associated with the permission set you want them to consent to:
Verify that the associated Enterprise application is installed and reinstall it
Follow the guide to revoke consent to a permission set, and if you find the enterprise application at step (3), delete it.
Then, follow the guide to consent to the necessary permission sets using a link in the article, How a global or privileged role admin can consent to ShareGate's Microsoft 365 permission sets.
ShareGate Migrate
If the permission set was consented to and the change is not reflected in ShareGate Migrate, try reconnecting your tenant in Explorer.
If the reconnection does not work and you connect with Browser authentication, you can try turning Single Sign-On (SSO) off, as it can prevent ShareGate Migrate from confirming consent was granted in some cases.
Contact our technical support team if you experience further problems with consent to ShareGate's Microsoft 365 permission sets.