I have a project that was created on a 350 x350 mm, if I reduce the size of the parts the cut lines where the pieces fit together reduce, since the board is 3 mm thick it will obviously not fit together anymore. Is there a way to get all the lines adjusted without doing one by one. Sorry I am a complete newbie and still trying to figure it out. Attached is the svg file I mean and a picture of the issue.

Its a downloaded file , modified in newly installed inkscape on a windows 11 box 

Thank you for your guidance. 

Actually, this is not too hard.

you are super helpful , Thank you very much @Paddy_CAD