How to "un-strangle" a seat tube?

[foxb13]

Works on really thin sheet, not here.

Paintless dent removal uses a hot glue instead of weld to achieve a similar result.

And also suction cups. That won't work either here.

 

[DrmZ]

I remember vaguely a Paul Brodie Video on his youtube channel where he fixed a dented tube. If I remember right, he did it with two wooden blocks where the inside of each half was milled in the diameter of the tube. By clamping the tube between these wooden blocks in a vice and turning the frame/tube he pushed out the dent.

 

[novocaine]

this is the tooling (sort off)

https://www.ebay.co.uk/itm/40571167...MI987B9PiijwMV95VQBh1usw1jEAQYBCABEgLZpPD_BwE

you need to make an extension for it to reach that far down. A socket extension works fine, but you want it semi permanently attached so you can pull it back out afterwards.
you use some gentle tapping with the right size hammer to move the material around. the material has stretched, so don't expect perfect.