How can I go back from A7 to A6 on vernee thor

[AC Question]

I have vernee thor updated to A7.All is fine,but I could use my phone for calling only 3-4 times when it is OK.After 3 - 4 times calling I hear the oposite side,but they don't hear me.That's why I want to go back.How can I do it?

 

[belodion]

It may be best in the first instance to contact the manufacturer's customer support, since that device is not generally well-known, though it may be locally so.