This SOL could be interesting for you - https://support.f5.com/kb/en-us/solutions/public/14000/700/sol14783.html
Create a new (custom) clientssl profile where you specify
1) Cert
2) Key
3) Chain (Cert of the authority intermediary who signed your CSR, i.e. DigiCert CA).
For Chain, import the Intermediary CA as any other regular Certificate. Before doing so, make sure you have the correct type of Intermediary CA which matches your certificate Issuer Name 1 to 1; you may run into issues if you use incorrect type. If unsure, ask for the correct Intermediary CA Certificate from the same person who sent you the Signed Public Certificate.
When you're finished with the creation of your custom clientssl profile, go back to Virtual Server settings, and apply it as `clientssl profile`; click Update. Done!
It's never a bad idea to finalize certificate updates by validatating with your favourite online SSL checker, i.e. www.digicert.com/help
It will let you know if the certificate is correctly installed.