many have dogs that will play/go-get the toy but not return it, but I take it you are really dealing with a dog that isn't motivated to go even that far, so you want to break the whole process into as many small steps as possible, keep sesssions brief/fun, go back a step if any confusion arises...
you can hopefully find something the dog will hold in her mouth, like a small rope tug or tennis ring. then first step is teaching her to 'give' but you have to go back a step & teach her to 'take' on command, & there is even a step before this! You may have to start with 'touch'.
Present the toy & if she even puts her mouth toward it say 'yes' with enthusiasm & give her a treat. Repeat this until she really is eagerly touching, then you can say the command 'touch'. then gently insist she take it in her mouth. you get the picture.
depending on her attitude, like if she is used to being handled & not sensitive, you could even gently pry open her mouth by putting a bit of pressure on her lips, like you might be giving a pill. the key is to say 'yes' & treat the instant she is opening her mouth whether on her own or with your assistance.
after you are getting good results & she is enjoying this game, then you can hold the toy further away, saying 'touch' ('yes'treat')then 'take'('yes'treat)
one thing, when you do get as far as tossing the toy, you might want to have her on leash in case you need to gently pull her back to you.
you can use 'take' for the other commands like fetch or get-it, but when she does get it in her mouth, you will start on 'give' & for her bringing it back to you 'bring'
in time you can also have her 'wait' 'find-it' retrieve it from 'under' something, 'catch-it'
this is a wonderful game with many variations that I give my dogs credit for teaching me!
1 more tip (sorry) but some dogs learn from watching another dog