There are lots of suggestions on this subject in that topic here Improve Dual-SIM support - #5 by lzbk
Other topics deal with this (or bugs related to SIM card choice) :
- Bluetooth and Car Kit and Dual-SIM: calling (still) unreliable/random
- XA 2 dual sim: Bluetooth Audio / Car not working if second simcard active with SFOS 3.4.x and previous
- Secondary users and dual SIM usability
- Naming of Dual SIM cards
- Dual sim: Identify incoming call
- [4.0.1.45][XA2 plus dual sim] - sim not selectable
- Dual sim network / phonecall splitting? does this work?
- Dual-sim mobile phones: dissociate uses by cards and simultaneous activation of 2 cards in transmission and reception