I want to link my Instagram with my IMDbPro account

Official SNS accounts for any person can be added by anyone to the person's "Official sites" links by editing the person's page. I don't think has anything to do with paying for Pro or whether it's the page about yourself or not, but staff might be able to correct me on that.

Though guide for links to external sites for Names doesn't specifically mention Instagram or TikTok, I've found that they can be linked to in the same format as other SNSes, with "Instagram" or "TikTok" as the description, and the links get approved.