If the seedlings were spaced well in the seedling tray, you should be able to separate their roots without too much difficulty. I like to pop the entire mass of plants out of the seed starting tray and tease apart the roots with a pencil. Be sure to handle the tender seedlings by their leaves rather than grabbing the delicate stems, which can easily be crushed. Rather than transplanting these little seedlings directly into the garden, you’ll have better luck potting them up into individual pots or cell-paks first. Grow the separated seedlings in the individual containers for several weeks to reestablish a healthy root system, which will more likely withstand transplanting into the garden.