In a toy environment, this is a choice you can make relatively freely, depending on what you want to achieve with the learning challenge.
It may help if you think through what the actual consequences for making the "wrong" move are in your environment. There are a few self-consistent options:
The move simply cannot be made and count as playing the game as intended. In which case, do not allow the agent to make that choice. You can achieve that by filtering the list of choices that the agent is allowed to make. In DQN that will mean supplying an action mask to the agent based on the state so it does not include the action at the stage it makes a choice. This "available actions" function is usually coded as part of the environment.
The move can be attempted, but results in no change to state (e.g. the agent bumps into a wall). If the goal is to reach a certain state in shortest possible time, then you will typically have 0 reward and a discount factor, or negative reward for each attempted action. Either way, the agent should learn that the move was wasted and avoid it after a few iterations.
The move can be attempted, but results in disaster (e.g. the agent falls off a cliff). This is the case where a large negative reward plus ending the episode is appropriate. However, don't use infinite rewards, positive or negative, because that will cause significant problems with numeric stability. Simply large enough to offset any interim positive rewards associated with that direction should be adequate. For a simple goal-seeking environment with no other positive rewards than reaching the goal, ending the episode early is already enough.
When you don't have a toy environment where you get to decide, then the three basic scenarios above can still help. For instance, in most board games we are not interested in having the agent learn the rules for valid moves when they are already supplied by the environment, so the first secnario applies - only select actions from the valid ones as provided by the environment.