It depends on what changes you made. The simple start is to recreate tne normal.dotm template. With Word closed, rename the existing template. Then open Word.
If that doesn't fix your problem, write back with exactly what was changed and I or someone else will tell you how to get it back.
Normal Template in Microsoft Word - How to Find or Open the Normal Template

For an idea of where else changes get stored, take a look at Word 2007 & Later Key Data File Locations.