After completing a swap transaction, how do I update the liquidity amount L?

[vball]

Do I need to recalculate the liquidity amount L and record the reduced portion?

[OoXooOx]

Yeah, it's not clear from 1 milestone, but you can check code of milestone_6.
In swap function in UniswapV3Pool you can see how we work with liquidity.
uint128 liquidity_ = liquidity;
if (zeroForOne) liquidityDelta = -liquidityDelta;
state.liquidity = LiquidityMath.addLiquidity(
state.liquidity,
liquidityDelta
);
if (liquidity_ != state.liquidity) liquidity = state.liquidity;