1944 German occupation, returned field post letter of Russian serviceman, (Narva – ) Riga, Latvia – Narva

Interesting item addressed to Riga, Latvia, but returned from there as recipient unknown. The sender is Russian in German forces, return address on the back of the cover is in Narva, Estonia and the one written in the included letter is German field post 08762, likely Feld-Nachrichten-Kommandantur 52. Looks like the letter was actually posted in a collection box in Riga and then supposedly returned to Narva, Estonia.