EEG position template

I am a new Brainstorm user. I have a problem with adding EEG positions template. I have 19 participants. The data was recorded by 10-20 system 64-electrode ant cap. But 4 of the participants are recorded by a different old ant cap. In the ".vhdr" file, there are 88 electrodes for only the 4 participants, 64 normal electrodes and 24 electrodes named "BIP1+" to "BIP+24".
I imported the data into brainstorm, I choose "Add EEG position"--> "ICBM152"-->Brainproduct Easy Cap M1 for all the participants and the positions were found. Even though I use the same template, I could not average the 19 participants together because the error says they have different data matrix. I want to ask is it possible to do the average under this situation? (I tried to delete the electrodes in the time series, but it doesn't work.) Could you please help with this? Thank you so much.

To average recordings, you need the number and names of data channels to be the same across across all files. To remove extra channels or add missing ones, select all the recordings in Process1 and use the process "Standardize > Uniform list of channels".
You cannot undo this operation and there is a high chance of manipulation errors, so make sure you backup your database before trying this.

Hi, Francois,
It works well. Now I can average my data. Thank you so much for your reply.