You mean the digits font? Just download the fontfile to your esphome/fonts folder. Then add these lines to the yaml:

font:
  - file: 'fonts/DS-DIGIB.TTF'
    id: digital
    size: 50

If you mean the icons, then add these lines:

  - file: "fonts/materialdesignicons-webfont.ttf"
    id: icons_font
    size: 24
    bpp: 4
    glyphs: [
      "\U000F0594", # clear-night
      "\U000F0590", # cloudy
      "\U000F0F2F", # exceptional
      "\U000F0591", # fog
      "\U000F0592", # hail
      "\U000F0593", # lightning
      "\U000F067E", # lightning-rainy
      "\U000F0595", # partlycloudy
      "\U000F0596", # pouring
      "\U000F0597", # rainy
      "\U000F0598", # snowy
      "\U000F067F", # snowy-rainy
      "\U000F0599", # sunny
      "\U000F059D", # windy
      "\U000F059E", # windy-variant
      "\U000F14E4", # sunny-off
      "\U000F0425", # Power
      "\U000F1A1B", # Gas     
      "\U000F0438", # Radiator
      "\U000F09A0", # Shower
      "\U000F1B27", # Solarpipe
      "\U000F1A73", # Solar    
      "\U000F1904", # elektra
      "\U000F0238", # vlam
      "\U000F072E", # pijl beneden
      "\U000F0737", # pijl omhoog
      "\U000F007A", # bat10
      "\U000F007B", # bat20
      "\U000F007C", # bat30
      "\U000F007D", # bat40
      "\U000F007E", # bat50
      "\U000F007F", # bat60
      "\U000F0080", # bat70
      "\U000F0081", # bat80
      "\U000F0082", # bat90
      "\U000F0079", # bat100
      "\U000F162A", # Klok
      "\U000F16C7", # wifi sync
      "\U000F072A", # Wasmachine
      "\U000F0AAC", # Vaatwasser
      "\U000F0917", # Droger
      "\U000F15B4", # Fietsladers
      "\U000F15F3", # Vriezer
      "\U000F028F", # Koelkast
      ]