Hello,
you would need to comply with FCL.510.A
General rule is that your operator has approval to log those PIC(US) - pilot in command (under supervision) for copilots. In europe it is so-called copilot development program. Usually those hours are credited devided by 2 to get a credit towards PIC requirement.
Should you have any questions, contact me, I am EASA examiner and also TRE
FCL.510.A ATPL(A) — Prerequisites, experience and crediting
(b) Experience. Applicants for an ATPL(A) shall have completed a minimum of 1 500 hours of flight time in aeroplanes, including at least:
(1) 500 hours in multi-pilot operations on aeroplanes;
(2) (i) 500 hours as PIC under supervision; or
(ii) 250 hours as PIC; or
(iii) 250 hours, including at least 70 hours as PIC, and the remaining as PIC under supervision;
(3) 200 hours of cross-country flight time of which at least 100 hours shall be as PIC or as PIC under supervision;
(4) 75 hours of instrument time of which not more than 30 hours may be instrument ground time; and
(5) 100 hours of night flight as PIC or co-pilot.
Of the 1 500 hours of flight time, up to 100 hours of flight time may have been completed in an FFS and FNPT. Of these 100 hours, only a maximum of 25 hours may be completed in an FNPT.