According to the post here …
You’ll likely need to contact those moderators mentioned in order to change your username. They are @Shradha_Upadhyaya and @Roxana_Stratila
Looks like just some emails back and fourth… but you’re right that there’s not a way on the site from what I can see!
ashokkarale
MD_Farhan1
Ajay_Mishra
postwick
Dheerendra_vishwakarma
Anil_G
chandreshsinh.jadeja
Gautham_Pattabiraman
vrdabberu
aravindbalineni123