Why is my name greyed out

Hi my name is greyed out on my iPhone 11. I have a message that I can’t receive iMessages because I’ve been signed out but I don’t know how to sign back on? I’ve tried to turn on imesssages but I can’t because it is greyed out. It also says that iCloud and iMessage are different. But doesn’t say where or how to make them the same. I have tried taking out the SIM card and putting it back in. I’ve also shut down the phone and done both of the above at same time and nothing changes it from being greyed out