make Polygon near by Multypolygon?

Hello dear friends!

Pls, may wonder how can i, and ever i create a polygon (woods) by drawing a line (white one without tags) in web0-editor iD?

if i delete dependencies from lake-coast (wich is multypolygon by itself) and then cut it on fist and second forming dot's - then i can create new multypolygon from 2 lines but after doing so - lake is gone completely

Hope for help

• Maybe anyone can reccomend YouTube or other sources tutorial video's for web-editor iD?

Thank you