Mobile ticket(s) are transferable and can be transferred directly through the third party the ticket(s) were accepted through (Ticketmaster, AXS, SeatGeek, team or venue in most cases). All you will need is the attendees name, email address and/or mobile phone number. Once transfered the recipient will need to follow the same process you did to accept the ticket(s) in the first place. Do not send screenshots as many venues use rotating barcodes where the QR/barcode is changed every so often for security purposes.
Electronic PDF tickets can just be sent to the new attendee. The name on the ticket will not matter, the venue will only scan the barcodes.
Any physical tickets such as hard-stock or a wristband will need to be delivered to the new attendee. The format of the ticket is unbale to be changed.