Once the analysis is done, you can click on any error message and the error in the text is selected. So it is very easy to reach the error. Isn't it working for you? If your layout is complex (you have tables,etc.), it's possible that it doesn't work.
There is a limit for large documents, because of a server restriction. If your text is longer than 15000 characters, you need to select previously some part of the text.
Again, it should be very easy. If LanguageTool has a suggestion, just clicking on the suggestion (yellow buttons) should replace the error with the suggestion. Perhaps in documents with a complex layout it doesn't work. Could you share some document with this problem?