Hi Aly,
It should be possible to update (PUT) your API using Tyk OAS, as described in Update an OAS API.
An example Petstore PUT Payload would looks something like
{
    "info": {
        "title": "Petstore",
        "version": "1.0.0"
    },
    "openapi": "3.0.3",
    "paths": {
        "/pet": {
            "post": {
                "operationId": "addPet",
                "responses": {
                    "405": {
                        "description": "Invalid input"
                    }
                },
                "summary": "Add a new pet to the store",
                "tags": [
                    "pet"
                ]
            }
        }
    },
    "components": {
        "securitySchemes": {
            "jwt_auth": {
                "bearerFormat": "JWT",
                "scheme": "bearer",
                "type": "http"
            }
        }
    },
    "security": [
        {
            "jwt_auth": []
        }
    ],
    "servers": [
        {
            "url": "http://127.0.0.1:8080/"
        },
        {
            "url": "https://petstore.swagger.io/v2"
        }
    ],
    "x-tyk-api-gateway": {
        "info": {
            "id": "ff70c9eb17644ba9895d9f2521637ff7",
            "name": "Petstore",
            "state": {
                "active": true
            }
        },
        "upstream": {
            "url": "https://petstore.swagger.io/v2"
        },
        "server": {
            "listenPath": {
                "value": "/",
                "strip": true
            },
            "authentication": {
                "enabled": true,
                "securitySchemes": {
                    "jwt_auth": {
                        "enabled": true,
                        "header": {
                            "enabled": true,
                            "name": "Authorization"
                        },
                        "identityBaseField": "cid",
                        "policyFieldName": "pol",
                        "signingMethod": "rsa",
                        "source": "aHR0cDovL2p3a3MudXJp"
                    }
                }
            }
        }
    }
}