Latvia – Zelta Zivtinja (prepaid) does not support call forwarding (number parking), thus not letting you keep your number with Roamer abroad. Roamer will offer you to use a different Latvian number instead.
You can now switch from ZZ to Tele2 at Tele2 offices, some of ZZ plans have an equivalent in Tele2. It is the same company btw.
All of the other operators/plans/cards in Latvia (LMT, Tele2, Bite, OKarte) DO SUPPORT call forwarding (number parking).
Please do not forget to park your number BEFORE departure. Should you wish to cancel the forward you will be able to do it anytime regardless whether your are located in your home country or abroad. Once the parking (forward) is cancelled you will not be able to use your Latvian number with Roamer anymore in this particular trip.