The procedure is on page 70 of BEA#1:
1.18.4 Procedures to be applied in case an unreliable speed indication is detected
On the date of the accident, the operator’s procedures mention that the following actions must be carried out from memory by the crew when they have any doubt concerning the reliability of a speed indication and when control of the flight is “affected dangerously”:
(...)
If conduct of the flight does not seem to be affected dangerously, the crew must apply the UNRELIABLE SPEED INDICATION / ADR CHECK procedure (see appendix 9).