From all the issues that you can have with canvases this is one of
the most common and easy to fix, in only 3 steps your canvas will look like brand new.
This is how my canvas looked after I misplaced it on top of spray cap :(
How to fix a dented canvas in 3 easy steps:
1) Pour a small amount of water on the back part of the canvas dent.
2) Spread it with the help of a clean cloth or fingers(remove excess)
3) Let it dry and see the miracle, your canvas is now dent-free.1)Pour a small amount of water on the back part of the canvas, just a small amount we don't want to get the whole painting wet, also remember to only wet the area with the dent just like in the picture below.
2) Spread it with the help of a clean cloth or fingers, this is just to spread the water through the canvas, do it so just in the surrounded area of the dent, this will help with the absorption of the water, this will basically help the canvas to go back to be flat, after all the canvas is just fabric, do not pour anything else, just water, otherwise you can damage the canvas.
3)Let it dry and see the miracle, your canvas is now dent-free. Do not use hairdryer or if you need it done faster, use it but keeping a good distance from the canvas, the best way is just let it dry naturally in a well ventilated and not too humid room, hopefully with access to sunlight.