How to give like on youtube using youtube.api.v3 or after elements on the page?

I think you can use HtmlAgilityPack library to get id or class of youtube website, then login with your google account. You can press like or dislike automatically.

HtmlAgilityPack is an agile HTML parser that builds a read/write DOM and supports plain XPATH or XSLT. It's a .NET code library that allows you to parse "out of the web" HTML files.

The parser is very tolerant with "real world" malformed HTML. The object model is very similar to what proposes System.Xml, but for HTML documents.