Tutorial:Blinking

First, you need to have eyes to scale. I'm gonna store them in a variable for easier accessing, as well as how fast I want to blink (in ticks) and the height of my eyes in blockbench units. Your path will be different

local eyes = models.model.root.UpperBody.TheHead.Eyes
local EYE_HEIGHT = 2 --The height of your eyes in blockbench units
local BLINK_RATE = 4 * 20 -- 4 Seconds

Next, you want to create a TICK event to set when my eyes blink, as well as 5 variables: tick, oldScale, newScale, oldPos, and newPos, initialized as shown

local oldScale = vec(1, 1, 1)
local newScale = vec(1, 1, 1)
local oldPos = vec(0, 0, 0)
local newPos = vec(0, 0, 0)

local tick = 0
function events.TICK()
  -- Sets old pos and scale for later interpolation
  oldPos = newPos
  oldScale = newScale
  tick = tick + 1

  -- If time to blink, set new position and scale to close the eyes, otherwise open them
  if tick % BLINK_RATE == 0 then
    newScale = vec(1, 0, 1)
    newPos = vec(0, EYE_HEIGHT / -2, 0)
  else
    newScale = vec(1, 1, 1)
    newPos = vec(0, 0, 0)
  end
end

Finally, you want to create a RENDER event to make the blinking smooth

function events.RENDER(delta)
  -- This interpolates the blinking to make for a smooth blink
  local scale = math.lerp(oldScale, newScale, delta)
  local pos = math.lerp(oldPos, newPos, delta)

  eyes:setPos(pos):setScale(scale)
end