Begin by familiarizing yourself with Slack's API documentation. This will help you understand how to access data such as messages, channels, or users from Slack. Ensure you have a Slack app created with the necessary scopes and permissions to read the data you need.

Create a Slack app in your workspace. Go to the Slack API website, create a new app, and configure it by selecting the necessary permissions (OAuth scopes) that allow you to read data. Install the app to your Slack workspace to generate access tokens.

Use Slack's Web API to retrieve the desired data. For example, you might use the `conversations.history` method to fetch messages from a specific channel. Write a script in your preferred programming language (such as Python or JavaScript) to call these API methods using the access token generated in the previous step.

Process the data extracted from Slack to a format that is compatible with Convex. This might involve converting JSON data to a specific data structure or format required by Convex. Ensure the data types and structures are consistent with what Convex expects.

Create a Convex project if you haven't already. Set up your database schema to accommodate the data you plan to import. Define tables and fields in Convex that match the structure of your processed Slack data.

Develop a script to import the processed data into Convex. Use Convex's API or SDK to write data to your database. This script should iterate over the data and insert it into the appropriate tables in your Convex database.

After importing the data, verify that it has been correctly stored in Convex. Use Convex's querying tools to check the data integrity and ensure that all data fields have been accurately imported. Perform tests to validate that the data behaves as expected within your Convex application.
By following these steps, you can manually move data from Slack to Convex, leveraging each platform's API capabilities without relying on third-party connectors.