Run the following command to apply the commit to your container:
curl https://github.com/EGroupware/egroupware/commit/a9dc772e141e37fa06ac8cbaf5dc98857478a480.patch | docker exec -i egroupware patch -p1 -d /usr/share/egroupware
docker exec -it egroupware kill -s USR2 1
If that works, you can make the commit permanent (not lost after contaienr restart) by running:
curl https://github.com/EGroupware/egroupware/commit/a9dc772e141e37fa06ac8cbaf5dc98857478a480.patch | docker exec -i egroupware patch -p1 -d /usr/share/egroupware-sources
Ralf