Delete lines

You need to better explain what kind of "shape" you're referring to. The answer will vary greatly depending on that bit of information.

Hi there

Hope you are doing well and sorry for the trouble.

Would you mind sharing the steps you did to create/draw the shape? 

If you have used the Pencil Tool to draw the shape, to erase parts of the drawing,  Go to Tools > Comment  and select the Pencil Eraser tool and drag across the areas of the drawing that you want to remove.

For more information please check the help page https://helpx.adobe.com/acrobat/using/commenting-pdfs.html

Regards

Amal