In the desired affix entry, click Allomorphs field.
Click the menu button 
that appears, and then click Insert Affix Process.
Enter the affix allomorph.
Select a morph type.
In Lexicon Edit, you can insert a new allomorph with an Affix Process Rule field. You can also convert an entry or an alternate form to have an Affix Process Rule field, or delete the Affix Process Rule field (by a reverse conversion).
In the desired affix entry, click Allomorphs field.
Click the menu button that appears, and then click Insert Affix Process.
Enter the affix allomorph.
Select a morph type.
See 
Important below.
In the desired entry, do one of the following:
To convert a lexeme form, click the Lexeme Form field label.
To convert an allomorph, click the Affix Allomorph field label.
Click the menu button that appears, and then click Convert to Affix Process.
An Affix Process Rule field appears. The menu command changes to Convert to Affix Allomorph.
To convert a process affix entry or allomorph back to a regular affix entry or allomorph, do the following:
Right-click the desired Lexeme Form field or Affix Allomorph (Process) field, and then click Convert to Affix Form or Convert to Affix Allomorph.
The Affix Process Rule field is removed, and the Environments, Required Featured, and Infix Position fields are restored for the lexeme form or for the allomorph.
When you do the convert steps above, the affix entry (lexeme form) or affix allomorph is converted to an affix process entry or allomorph.
Convert refers to the change that enables the following functionality:
Instead of merely saying, for example, that "-um-" is an infix and it can occur in these positions: / # [C] _ or / # _ [V]", that there is a process that matches this sequence of segments and converts them to another sequence (including inserting "-um-" at the appropriate place).
The conversion removes the Environments, Required Features and Infix Position fields and does not keep track of any existing contents.
The Is Abstract Form field becomes selected.
An entry can have a mix of regular affixes and process affixes. An entry can also have more than one process affix, for example, in cases where different inflection classes have different infixation processes.