There are no direct instructions in the EASA regulations on how to correct a CRS, like there are for correcting an EASA Form-1. That is because a CRS is not a predefined EASA Form and has therefore no pre-defined lay-out, like an EASA Form-1 has.
The only things required for a CRS (lay-out and correction) is detailed in EASA Part-M.
M.A.801 (e) A CRS shall contain at least:
basic lay-out of the maintenance carried out; the date on which the maintenance was completed; the identity of the organisation or person issuing the CRS, including, alternatively: (i) the approval reference of the maintenance organisation and the certifying staff issuing the CRS; (ii) in case referred to in point (b)(2), the identity and, where applicable, the licence number of the certifying staff issuing the CRS; the limitations to airworthiness or operations, if any.
EASA Part-M details in M.A.305 (a) and (g) that:
(a) At the completion of any maintenance, aircraft certificate of release to service (‘CRS’) required by point M.A.801 or point 145.A.50, as applicable, shall be entered in the aircraft continuing airworthiness record system, as soon as practicable and no later than 30 days after the completion of any maintenance.
(g) All entries made in the aircraft continuing airworthiness record system shall be clear and accurate. When it is necessary to correct an entry, the correction shall be made in a manner that clearly shows the original entry.