Preprocessing text so that two words without a separating space (or hyphen separated) are detected
Two possible strategies:

Hard coded rules

Statistical learning


Hard coded rules means creating a mapping from original text to the normalized representations.  The text will have to be manually inspected to find commonly occurring patterns. Hard coded rules are often done with regular expressions.
A statistical learning approach looks for patterns in the data. Bigrams can be defined as the conditional probability of a token given the preceding token. When that probability is above a threshold the two tokens are merged.