Hi,
There is a variable, "last_lost" which is the amount lost since the last win, which I think is what you want.
Set up a "set user variable"
amt_to_bet = default_backa + last_lost
or however you want to calculate the amount to bet. Could be
amt_to_bet = default_backa + 1.10 * last_lost
to recover 110% of what you have lost.
NOTE: You don't really use the equal sign, but rather use the variable name and value parts of the "set user variable" trigger.
Then use a "back" trigger on Favourite, with amount "amt_to_bet".
As ever, try in test mode first.
Jim