It is usual to have possibility to post Credit Memo for any item you sold. You can also make Credit Memo for Fixed Assets you sold. Generally, you can use the same flowchart about using of posting groups, as I published for FA Sales Posting.

But G/L entries will not be the same (with opposite sign) as you got in FA sales posting process. You will get the following G/L entries:

Entries are a bit different in comparison with posted invoice. Entries in FA Ledger Entries also will be the different. You will get only Gain/Loss FA Posting Type entries in FA Ledger Entries with Credit Memo Document Type. That means, you must create additional Acquisition and Depreciation entries manually, if you want to have Fixed Asset again in your system.