Given that you have a badge in the community, I presume that you both passed the CISSP exam and completed the endorsement in April. This implies that your CISSP "three year cycle" begins May 1, 2022 and ends April 30, 2025.
One of the "gotchas" is that one must earn the continuing education credits duringyour "three year cycle" for the certificate to which you will be applying the credits. So, starting next week, any effort you expend studying for the CCSP could potentially apply to the CISSP, but none of it would apply to the CCSP (because its does not yet have a 3 year cycle).
I say "potentially" because another gotcha is that CPE credits must be related to one or more of the domains for the certification to which they are being applied. So, to truly credit studying for CCSP, the material would also need to be related to both CISSP (which is likely the case).
Links PLEASE - you stated use EDUCATION tab and then a webinar to apply external credits. However, there doesn't appear to be an EDUCATION tab anymore and webinar takes you to predeveloped courses without option to send in any external education certificates.