Hi. You can place U bricks that are for chaining. This prevents you from having to form. You make a row with them and before filling with concrete place two irons of Ø 8 mm. regards
https://articulo.mercadolibre.com.ar/MLA-627806523-bloques-ladrillo-de-hormigon-cemento-u-13x19x39-pencadenado-_JM