What you need is the model number of the enlarger chassis (D2, D5, DII, D6 or ??), and then the instruction manual for that model.
The instruction manual will have instructions on aligning the enlarger.
Harry Taylor is a good suggestion - here is a link to his website: http://www.classic-enlargers.com/. Most likely you will be able to obtain both a manual and advice from him.
Another good source is KHB Photographix (referred to by Harry as "the Canadians"). Their website is here: http://www.khbphotografix.com/. They too are a great resource for both a manual and advice.
Both sources may be able to recommend someone to do the alignment for you.