When you replace a larger chainring (44T) with a smaller chainring (38T) on your EMTB, it may be necessary to shorten the chain as well. The reason for this is that the smaller chainring will take up less space on the chain stay, which means that the chain may be too long and may be at risk of falling off the chainring.
To shorten the chain, you will need a chain tool to remove one or more links from the chain. It's important to ensure that you remove an even number of links, to keep the chain's structure intact. You can also use the bike's gears to help you determine how many links you need to remove by moving the chain to the smallest cog on the rear cassette and the largest chainring in front. This will allow you to see how much slack is in the chain.
Keep in mind that you'll want to make sure that the chain is not too tight, as this can cause damage to the chain and gears. Therefore, you should make sure that the chain has enough slack so that you can easily move the derailleur in and out, but not so much that it can fall off the chainring.
It's always better to have a bike shop or professional mechanic to do the job if you are not confident with the process, they have the right tools and experience to do it properly.