First, you need to create a offset entry (Outgoing) and match it with the liability in CZK.
Next, create a second offset entry (Incoming) and match it with the receivable in EUR. Make sure to enter the correct exchange rate so that the amounts match exactly.
To link these two offset entries, the offset number is key — it must be the same for both entries.
Once the same offset number has been entered, you can verify that the entries are correctly linked, for example, in the print report "Mutual Receivables Offset Agreement".