If you are already active in a voluntary organisation you can enquire about possible training schemes there. In case there are no regular meetings to reflect on and examine your voluntary work, you could suggest such a meeting (possibly under professional guidance).
The following organisations offer training schemes and workshops concerned with voluntary support for refugees:
If you want to become a refugee buddy or sponsor you can learn a lot about volunteering as a tandem during seminars or workshops. This way you can get prepared for your voluntary involvement. Currently, the following organisations offer this training: