Left headphones suddenly quieter?

I use the Huawei Freebuds Lite (for 3 months). For a few days now, much less sound has come out of the left headphone than from the right. I have reset and updated the headphones dozen times, but without improvement. How can this be? Is there anything else I can do or should I send it back directly to the dealer?

The dealer is Lidl. I bought it on 02/29/2020.

For me, as disgusting as it sounds, it was just a matter of cleaning… That often helps a lot. If nothing changes, then only the return helps as long as the guarantee is on it.