First you need to create Custom field named "LEDES Classification" of type Dropdown list on Lawyer Subject like this:
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Then add 4 options like this:
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Those values have this meaning:
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AS - Associate (An associate is a lower-level professionally licensed attorney who does not hold an ownership interest in a law firm. )

OC - Of counsel (An attorney employed by the law firm who is not an associate or a partner but who is on track to become partner or who was previously a partner and is now retired.)

OT - Other - (A status to indicate a system user who does not provide services that are billed to the client)

PT - Partner - (A partner owns and directs the business of a law firm and may be either an equity or non-equity shareholder. )

And fill this field for every user. If no value is filled, PT is used by default.
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In invoices overview, filter out those you want to export to Ledes format and than click on small down arrow next to download button and choose LEDES 98B