Backup ... (almost) Everyone else seems to assume that you are doing Direct To Garment printing (DTG). Your printer is one of those Epson WorkForce multifunction printers, so I doubt you are doing DTG with it. That means you are doing inkjet transfers, correct?
Your problem is probably letting the printer manage the color rather than using a color profile specific to the transfer paper you are printing on. First step is to download profiles from the company that makes the transfer paper. (If they don't provide any, you can get by with using the closest Epson profile.)
In your printer driver/setup, turn OFF color management.
In your graphics application (probably in its print dialog, or advanced part of it), choose the option to have the application control the color management. Select the correct profile for your paper. Adjust other settings as recommended for use with that profile. Set Rendering Intent to Perceptual. If the colors look muted and lighter than expected, try Relative Colorimetric, but check to make sure you don't lose too much detail in the shadows or have end up with obvious artifacts.
Are you judging the output by what you see on the transfer paper, or what you see on the shirt? It will not look quite right on the transfer paper, so be sure to press onto a test shirt before judging. Also, the OEM Epson inks shift color balance when heated, but a profile made for your transfer paper and Epson inks would account for that.
Are you using an opaque paper or a paper for light colored shirts? The latter will show the color of the garment through the image, and is only color accurate on white shirts.
What piece of unholy poop do you have for a monitor?
Common everyday monitors are utter poop for color accuracy. And even if they were any good, one would need to profile the monitor itself to ensure that what you see is what you get. I'm sure that is not your actual/main-problem, but realize there are practical limits on accuracy unless you spend more money on a monitor and profiling hardware--you should be able to get by without this, most people do. Just remember that your monitor is not entirely accurate.