You can choose to copy and paste your entire bio into the box, if you only want to use one of the new fonts.
If you'd like to use multiple fonts, however, then you'll need to do this in stages like I did to achieve the profile text at the beginning of the guide. (Simply repeat step 2, step 3 and step 4 for each portion of the text in a new font.)
If you've decided to leave the social media hub, Instagram, you may want to delete your account. If you're looking for something less permanent, temporarily disabling your account might do the trick.