Remove interior panels?

Yes, you can remove them, can you give us more details?

how to remove the hatchback interior panel to service the parts inside it?

Sure I got you covered,

To remove the interior liftgate panel:

1. Open the rear liftgate.
2. Remove the liftgate pull strap/handle and its retaining fastener(s).
3. Remove the upper liftgate trim panel first.
4. Starting along an edge of the lower trim panel, carefully insert a plastic trim-panel tool between the panel and the liftgate.
5. Work around the panel, gently prying outward to release the retaining clips. Try to pry close to each clip so you don't crack the plastic clip mounts.
6. Once all of the clips have released, slide the lower trim panel upward. There are mounting hooks on the panel that must disengage before the panel can be removed.
7. Remove the panel from the liftgate.

For installation, position the panel over the liftgate, slide it downward to engage the mounting hooks, then align and press the retaining clips back into place. Reinstall the upper trim and pull strap.

I recommend using a plastic trim removal tool rather than a screwdriver because the older plastic panels and clip mounts can become brittle.

If you're removing the panel because the liftgate will not open, let me know. There is a slightly different approach we can use to gain access to the latch with the liftgate closed.

Check out the images below.

I cannot reach the fastener for the strap. There is no room between the panel and the strap fastener, even with the panel loose. How is that done?

Do you mean the screw is in too deep or is the strap just in the way. GM had some items that were not real thought out in those years. If it's that the opening is too small you may need a different tool, like a thin wall socket instead of a standard one or use a 1/4 drive instead of 3/8 drive. Can you take a picture and post it, perhaps we can give you an idea if we see the issue you are having.