access network share under another user account

Good morning , i have install comodo backup onto a windows 7 pro and i have created a share into my nas , shared with a specific user created for the backup purpose with no password change because i don’t want the pc user mess up with the backup file in case they find the share on the network.
the user on windows 7 pro is another user (not in the admin group) and when i setup the full disk backup i cannot pass the other credential to access the share.
how can i do this ?
at the moment i have added the pc user to the share because when i run the config of the job i need to access that share to save the file and also when i create the schedule for the differential backup i need to select a specific base but again if i don’t give access to the pc user to that share i’m not able to select the base image…
i don’t want to give the pc user to the share so i need to delete it but i need a solution…
thank’s in advance

maybe i have solved…created the backup user on that pc and configured the comodo backup on that user.
backup runs at scheduled time even the backup user is not logged with only pc user logged.
see if tomorrow will run again with no problem