I am looking to utilise my Amex PP companion voucher for a trip next year to South Africa (and beyond). We are currently looking to fly into CPT and then out of JNB on the return. Availability is OK for the dates we require based on return legs to each destination, however, how do I book the two separate legs, do I need to phone up BA to do this? Any tips and tricks here would be hugely welcome.

PS - The end of our trip is actually in the Seychelles, we are OK in theory to reroute to JNB but wondering if again there is anything we can do to optimise the SEZ return? Conscious we can book atm with avios on QR via DOH but we are unable to use the voucher here. Extra brownie points on offer to anyone who is able to assist!!