Dentist here. What to do sort of depends on the tooth.
If it is sensitive or an aesthetic issue you need to put the crown back on. Just carefully place it back on the tooth, it will only go one way. Sometimes it easier to get someone to help you. Use no force, ABSOLUTLY DO NOT BITE IT INTO PLACE. If you can get it off and on fairly easily then you can temporarily cement it. It can be done with denture adhesive or you can buy temp cement at the drug store. It is by the toothpaste. Only place a VERY thin coat on the inside of the crown. dry the tooth with a papertowel and place the crown. Be careful when eating, nothing sticky. Denture adhesive especially isn’t too strong. If you are eating and feel anything hard stop and do not swallow, you don’t want to swallow the crown.
If you aren’t worried about sensitivity or looks just leave it off. Should be fine until Monday. However you don’t want to leave it off much longer than that, as teeth can shift. Be careful when eating to protect the preped tooth.