@Audreylu92- I know this is 4 years too late for you and assume you've sorted this by now, but for others there are a few ways.
1) Using your existing certified SBC you can (license permitting) connect another SIP trunk to your 2nd carrier and then create an inbound routing rule to route all traffic into your downstream Teams DR trunk on the SBC. You don't need to create 2 Teams trunks (assuming the same Teams tenant is being used).
On the outbound trunk from Teams in your SBC, create routing rules that take the calling number from 2nd carrier pattern to then route to your 2nd carrier trunk.
2) Alternatively, there is a SaaS service that makes this easier for you that is point and click without deep technical expertise called Callroute. Check their tech article here: https://callroute.com/tech-blog/microsoft-teams/connect-multiple-carriers-microsoft-teams/
If you're a carrier though and want to connect multiple customer trunks to multiple customer Teams tenants then you have a few options
1) Direct Routing in the carrier trunk model (derived) which I can see you've already found the link for
2) Operator Connect
3) Callroute can also provide Option 1 aaS
Thanks,
Mark
