There is no direct command.
Depending how many variables you have available and whether you want the result in a single byte or each digit in a separate byte, there are several options.
1 You can use the BCDTOASCII and then subract $30 (ie "0") from each digit
BCDTOASCII b0, b1, b2 ; BCD value in b0, tens into b1, units into b2
b1 = b1 - $30
b2 = b2 - $30
b0 = b1 * 10 + b2
or
2. in simple maths using 2 varaibles
if b0 = 59 BCD and you want 59 decimal or $3B (hex)
b1 = b0 / 16 * 10
b0 = b0 AND $0F + b1