If there's an access hole close to a dent that can't be accessed directly with a hammer and dolly, use something called a "pick tool" to push most of the dent up close to level where some careful massaging with a smooth faced body hammer can be used to minimize the distortion. Be aware that a dent of more than a very small size will stretch the metal, making it difficult to put it back into its original shape without "oil canning"- - - -popping in and out with a slight push on the dented area.
Here's one example of a pick tool. Most well-equipped body workers would have an assortment of lengths and shapes, and sometimes it was necessary to drill a hole from the back side in double pamel sections close to a dent to use the tools. They're not just bent pieces of round stock- - -the good ones are spring steel.
https://www.ebay.com/itm/403531763396?Like a lot of other skilled trades, body workers who actually know how to straighten dents and metal finish their work are a dying breed! Now it's "cut, spot weld, and slap on the Bondo"!
Jerry
