place all your contacts from outside of Mastodon in a spreadsheet. Make sure you make these colums called "Name", "Email" and "Notified"

locate all your contacts outside of Mastodon and send them a direct message that you are closing your non Mastodon account and that @SusiArnott is your only social media, ensure you explain the reason such as Enshitification, additionally ask for their email. If they don't respond within 72 hours, might as well just delete them altogether.

update your spreadsheet, ensuring that you tick the Notified column for each an every contact and update the Email field should they respond to your direct message

within a week or so, close your non Mastodon accounts, breath a sigh of relief that you have successfully unloaded a massive weight, and finish it off with a glass of fine red wine.