You can always just make a decision to facilitate the flavor and direction of the story you wish it to have.
Do not be afraid to alter outcome resultes to enhance the suspense or heighten the feeling of the experience. You should NEVER set out to kill PCs. All things being equal, you should NEVER alter a check that directly results in killing a PC. The GM is NOT the adversary of the players – the GM is the teller of tales, there to ensure the action is balanced and fun for everyone in the group (including themselves).
Single Check Outcomes are Lethal: A checked outcome may also be assessed using Advantage or Disadvantage. This speeds up combat and emphasizes skill over luck, and is to be used unless noted in materials. It also rewards tactical planning and forethought in committing to combat because it is more lethal.
Determining Stock and Availability of Items
Stock Check: Determining whether or not a particular supplier or store has an item a character wants is up to the GM. If the GM needs to introduce an element of randomness, flavor, or risk, the stock check should be used. Their check may be augmented by additional funding, motivation, or game situation the character(s) finds themselves capable of leveraging.
Alter the Combat Challenges
Without having to go through and notate a lot of material, there is some very simple and easy things you can do, on-the-fly as a GM to make combat either more or less challenging to suit the specific PC’s. This is not something that you should just do because you can – there should be good reasons for doing it. Simply trying to make it easier for a group because they made bad decisions leading up to it is not very appropriate. Most often, it will be done universally – i.e. the particular adventure’s challenges are just too strong for the PC’s, but the GM wants to use the story thread, or it was just an inordinate amount of bad luck leading them to be ill-equipped to deal with the challenge at hand.