I created an OIDC - OpenID Connect web application on my Okta developer dashboard, after that, i set it up and integrated it to my web application.
Basically, users in my organizations can use the Okta integration to perform SSO on the web application as long as the users had been assigned to the OpenID app on Okta dashboard.
Now what i want is a way by which users from an external organization can get to perform SSO with Okta on my web application, with the credentials from their respective organization.
Kindly provide help on the steps i need to follow to make it happen.
You need to create an external SAML/OIDC identity provider in your own tenant, which will point to the customer's tenant/IdP. Depending on the login flow, you may need to create routing rules to instruct your Okta tenant, that some/all users have to be redirected to that external IdP for authentication.
Here is Okta documentation about using external identity providers.
Other option is to let that external tenant to have OIDC application created on their tenant and get it configured to use your application URL(s).