I deleted the portal to the end city in minecraft

Solution 1:

You can beat the ender dragon again to spawn a new, different end gateway, yes.
Alternatively, you can use /setblock to create one in the place of the old one, as explained below.

From the wiki page:

• The ExitPortal tag holds a set of X/Y/Z coordinates to determine the general location the player can be "safely" teleported to when entering.
• Setting ExactTeleport to 1 teleports entities to the specified coordinates exactly instead of at a safer location around those coordinates.

Example:

/setblock ~ ~-2 ~ minecraft:end_gateway{ExactTeleport:0,ExitPortal:{X:1000,Y:90,Z:3000}} replace

This will create an end gateway 2 blocks underneath you that exits at 1000 90 3000.