help to make an item that whem click on main hand, fix/heals up the durability of an item off-hand

I don't think you can simply use code blocks to achieve this functionality. You may need to write code in the use() function of your Item class. Here's some example code I wrote that can consume 1 durability point from a tape item and repair 16 durability points of another item held in the player's offhand. If the offhand item is not damaged or is also a tape item, the repair will not be attempted to prevent two tape items from repairing each other.

    @Override
    public InteractionResultHolder<ItemStack> use(Level level, Player player, InteractionHand hand) {

        // Get the itemStack that the player is holding need repair tool
        ItemStack itemStack = player.getItemInHand(
                hand == InteractionHand.MAIN_HAND ? InteractionHand.OFF_HAND : InteractionHand.MAIN_HAND);
        // Get the itemStack that the player is using as a tape to repair the tool
        ItemStack tape = player.getItemInHand(hand);

        // If the tool being repaired is damaged and is not RepairTape
        if (itemStack.isDamaged() && !itemStack.is(this)) {
            // Repair the tool being held by the player
            itemStack.setDamageValue(Math.max(0, itemStack.getDamageValue() - 16));
            // Decrease the durability of the tape itemStack
            tape.hurtAndBreak(1, player, (living) -> {
                living.broadcastBreakEvent(hand);
            });
        }
        return super.use(level, player, hand);
    }