Much of this will depend upon the type of track roller system you have.
The simple ones have an open faced track; that's the good news.
The bad news is that there are "captive" tracks; those are less prone to failure but also much harder to fix, because you've got to expose the track (take wallboard off).
If you're lucky, it's an open face unit .... Try this
First of all, it depends upon the failure mode
1) if both rollers (front and rear) are off the track
2) if only front roller is off
3) if only rear roller is off
Also, look up inside the track area and ascertain which is the "open" face of the track, so you'll know which way to move the rollers to engage them into the track
if you can get a small blade screwdriver under the lower edge of door, try to get the door slightly pulled out of the wall frame
then gently lift up on the leading (front - first in closing - whatever you want to call it) edge of the door from the lowest point with the screwdriver, and have a person help guide the roller onto the track. Once you've got the front roller engaged, pull the door out a bit more, then have that same someone hold the top of the door tightly (creating a pivot point around that engaged roller) and then you push the lower edge of the door back in towards the pocket. This will cause the door to rotate around that front roller, and make the rear roller tip "upwards" above and into the track. Takes some work, but it can be done.
Just do the first part of condition 1
Just do the second part of condition 1
There are some youtube videos you can watch as well.