This article describes how to merge users and content from one Slack channel with those of another. Since there is no real "Merge" option, you have to export and then import the channel and user data by hand.
Steps
Part 1 of 2: Export Channel and User Data
Step 1. Log in to your Slack team
If you haven't already, go to https://slack.com/signin to sign in now.
Step 2. Click
next to your profile photo.
It is located in the upper left corner of the screen. A menu will open.
Step 3. Click Team settings
Step 4. Click Import / Export Data
This is the button at the top of the window, next to "Settings & Permissions".
Step 5. Click the Export tab
The list of data types that will be exported should appear. These include message history, links to shared files, archived channels, and logs of integration activities.
You cannot export private group files and history, direct messages, and edit or delete logs
Step 6. Click Start Export
An export file will be generated. At the end of the operation, you will receive the notification that the file is available for download.
Step 7. Click the Ready for download [file size] link
It will appear at the end of the operation in the Export screen, under "Your team's exports". Your computer's Save dialog will appear.
Step 8. Open the desired path and click Save
The exported data will be downloaded to your computer. Once the download is complete, you can select that file and import it to another channel.
Part 2 of 2: Importing Data to Another Channel
Step 1. Open the page
If you still have the Export screen in front of you, just click the tab Import at the top of the screen.
Step 2. Click Information required
This is the blue button under "Current import". If you have exported more than one file, you will see them all appear on this screen; make sure you select the correct one before clicking the button.
Step 3. Map the users to import
Since you're not merging work environments, you shouldn't have to perform special operations on users. Select the item Map users when possible, and manually configure the rest from the drop-down menu under the heading "Users".
To change how users are merged, click the menu and select a different option. You can create a new account and invite the user, create an inactive account and invite them later, keep the user's messages or decide not to import them
Step 4. Select the channel information to import
Since your goal is to merge channels, click the drop-down menu next to the one you are exporting, select Add to an existing channel, then choose the second channel.
Step 5. Click Save Changes
You will now see the preview of the data that will be imported.
If you want to make last minute changes, click No, I want to change something.
Step 6. Click Yes, proceed with this import
The selected data will be imported to Slack. When finished, you will receive a confirmation email and the channels will be merged.
Step 7. Open the channel you just edited
The data of the old channel will appear together with that of the new one.
