No password on my instagram account?

Hello,

I have a second account which when I opened I linked to my main with a multi account login - therefore it never asked me to set a password. I then removed it from the multi account login system, and it never asked me to set a new password. The other day I accidentally logged out of the account and I can't get back in! It never asked me to set a password, so wtf do I do? It doesn't accept the same password as my main. PLEASE ADVISE I'M DESPERATE!