How to delete first voltage reading?
Simplest way is to have a flag to specify whether you've read the first reading or not.  Default to zero:

int read_first = 0;


Then you can say:

if (read_first ) {
    volt_V      = (resolution)*(float)sads1262Count;     // voltage = resolution * adc count
    Serial.print(volt_V,8);
}
else {
   // discarded first result, now we've read the first one
   read_first = 1;
}