Here's a little generic solution you might be able to use:

-- Create some sample data
create table tableName (field1 INT, field2 INT)

insert into tableName values (1, 2), (3,4)

create table anothertable(field1 INT, field2 varchar(30), field3 NVARCHAR(300))

insert into anothertable (field1, field2, field3)
select 1, 'test', 'another test'

declare @fields_to_clear table (
    name_like NVARCHAR(100)
,   field SYSNAME
,   field_value_to_set NVARCHAR(MAX)
,   id int identity
)

-- Here are the names and fields you want cleared
INSERT INTO @fields_to_clear (
    name_like, field, field_value_to_set
)
VALUES  ('%tableName%', 'field1', 'NULL')
,   ('%anotherTable%', 'field2', 'NULL')
,   ('%anotherTable%', 'field3', 'NULL')

DECLARE @SQL NVARCHAR(MAX)
,   @name SYSNAME
,   @field SYSNAME, @field_value_to_set NVARCHAR(MAX)
,   @start INT
,   @end INT

-- Get all matching tables and fields
DECLARE CR_X CURSOR READ_ONLY FORWARD_ONLY LOCAL STATIC FOR
    SELECT  t.name
    ,   field
    ,   field_value_to_set
    ,   ROW_NUMBER() OVER(PARTITION BY name_like ORDER BY id) AS sort
    ,   ROW_NUMBER() OVER(PARTITION BY name_like ORDER BY id DESC) AS sort_last
    FROM    @fields_to_clear fc
    INNER JOIN sys.tables t
        ON  t.name COLLATE DATABASE_DEFAULT LIKE fc.name_like COLLATE DATABASE_DEFAULT
    INNER JOIN sys.columns sc
        ON  sc.object_id = t.object_id
        AND sc.name COLLATE DATABASE_DEFAULT = fc.field COLLATE DATABASE_DEFAULT
    WHERE   t.is_ms_shipped = 0 -- just in case
    ORDER BY t.name, sort

OPEN CR_X
WHILE 1 = 1
BEGIN
    FETCH NEXT FROM CR_X INTO @name, @field, @field_value_to_set,@start, @end

    IF @@FETCH_STATUS <> 0
        BREAK
    -- Build SQL update string
    IF @start = 1
        SET @SQL = 'UPDATE ' + QUOTENAME(@name) + N'
     SET '
     if @start > 1
      set @SQL = @SQL + ','

      set @SQL = @SQL + QUOTENAME(@field) + ' = ' + @field_value_to_set

    IF @end = 1 -- Energize!
    BEGIN
        PRINT @SQL
        EXEC(@SQL)
    END

END
CLOSE CR_X
DEALLOCATE CR_X

select *
from tableName

select *
from anothertable
--Clean up sample data
--drop table tableName
--drop table anothertable

I create a little foundation table @fields_to_clear , which you can populate with table names as LIKE and name of fields you want to clear, and finally the value you want to set. I use NULLs, but in theory, you can also set them to 0 or whatever else. Just beware that strings might require extra quotes due to the nature of dynamic SQL.

Then i create a cursor which finds matching tables in the system catalog sys.tables and loops fields one by one. The loop builds the dynamic SQL which sets each field to the value in the field_value_to_set column.

You can comment the EXEC(@SQL) just to see the actual SQL being generated.

Be careful with the like-string so you don't blow away your whole database

You have to alias inline views in sql server. For example this works

Select *
From(select [name]
    From sys.tables
    where name like '%tableName%'
) as x