I am trying to access my voicemail, says there is a password but I don’t know what that means

Voicemail is a service of your cell carrier. Contact them for help with your voicemail password.

I changed sim cards from cdma to gsma and now cannot get into my voicemail. I put in my password and it does not work. I attempted to change my password but the link under phone is missing. Wi fi calling is off. I even reset my phone...still the blue link is not there.

Very upset. I have important messages need. Help asap.