Incorrect data messing with shapefile

Hi there, I recently downloaded a shapefile and loaded it using the Add Data button into ArcMap. However, I noticed that when I added the shapefile there is one data point way off of from where the rest of the data is gathered within Africa (for the record, the data contains geographical coordinates about "observations" in Africa). When I look into the wayward data point, I noticed in the attribute data that the longitude coordinate is -135047 instead of what it should be, -13.5047. I tried using the edit toolbar and went and changed the coordinate in the attribute table, but that does not change the projection (the data point still appears far away). I don't know if this will help but when I first add it to ArcMap I get this warning -

""Unknown Spatial Reference

The following data sources you added are missing spatial reference information. This data can be drawn in ArcMap, but cannot be projected.""

I know that it uses WGS 1984 and I think I know how to fix that issue once I solve the above issue (using the Define Projection tool is discussed here) but I thought I would include this information as well just in case the problems are related.

If you could please help me out that would be great!

Best,
Jeff